1. Field of the Invention
This invention relates to a process for the alkoxylation of compounds having reactive methylene groups. More especially, this invention relates to the preparation of such alkoxymethylene compounds by reaction of compounds having a reactive methylene group with excess orthoformic acid ester in the presence of a catalyst. This invention is particularly concerned with the preparation of alkoxymethylene compounds in substantially quantitative amounts where the alkoxymethylene compound is recovered in high purity.
2. Discussion of the Prior Art
L. Claisen, in "Berichte" 26, 2729 (1893), and Ann. 297, 19 (1897), described the condensation of orthoformic acid esters with compounds containing reactive methylene groups in the presence of acetic acid anhydride as catalyst. The mechanism of this reaction was thoroughly studied by Post, J. Org. Chem. 2, 260 (1937) and by Fuson, J. Org. Chem. 11, 194 to 198 (1946).
A description is furthermore given in U.S. Pat. No. 2,824,121 of the preparation of alkoxymethylene compounds from orthoformic acid triethyl esters and compounds containing reactive methylene groups, in the presence of acetic acid anhydride as catalyst. The preparation of this compound in the presence of excess orthoformic acid ester is also described in U.S. Pat. No. 4,058,553. In this method, carboxylic acids and their anhydrides as well as Lewis acids must be present as catalysts in order to obtain the desired high transformation together with good yields.
The first-named methods have the disadvantage that the reactions of the two reaction components with one another are incomplete, and numberous by-products form which considerably reduce the yield. The volatile by-products are, some of them, very difficult to separate by distillation from the alkoxymethylene compounds. The solid by-products reduce the yield and make refinement difficult. On this account the economical preparation of the pure alkoxymethylene serivatives is made difficult and in some cases impossible.
In the method U.S. Pat. No. 4,058,553, the simultaneous use of two different catalysts is disadvantageous. The amount of catalyst is accordingly relatively great.
It is an object of this invention, therefore, to provide an improved process for the production of such alkoxylated methylene compounds where the alkoxylated methylene compounds are obtained in a virtually quantitative yield. More especially, it is an object of this invention to provide an improved process for the production of such alkoxymethylene compounds which does not require a multi-component catalyst system. It is a further object of this invention to provide such alkoxymethylene compounds especially alkoxymethylene malonic acid derivatives in high yields and in high purity. These and other objects of this invention become apparent in the following description and claims.